Cement is very important as an ingredient of mortar, concrete and the like. Various cement additives have been investigated to date and commercially utilized for facilitating working of mortar and concrete and for improving the strength, water impermeability and other properties of concrete structures. The present invention relates to compositions and methods for improving the compressive strength of cement and gypsum products.
Gypsum is a common mineral (hydrated calcium sulphate, CaSO4.2H2O) used to make cements and plasters, especially plaster of Paris, walls, and sheetrock. Gypsum is also used worldwide in concrete for highways, bridges, buildings, and many other structures. Gypsum products include wallboard, plaster, plasterboard, molding, ornamental moldings, statuary, and architectural plaster work. There is a continuing need to increase the flexural strength of gypsum products to avoid cracking and breakage.
Cement, in various forms, has been used to bind materials together for centuries. However, the construction industry has been completely revolutionized since modern concrete was put into general use at the turn of the century. Although the two words concrete and cement are used interchangeably, cement is actually one of the ingredients in concrete.
Cement is a fine, soft, gray powder made from a mixture of limestone, clay, sand and/or shale. Making cement involves taking these natural materials, crushing them, burning this into clinker and grinding it into cement powder. When cement is mixed with water, it binds sand and gravel or crushed stone into a hard, solid mass known as concrete. Ordinary Portland cement is regular cement without any additives. Different types of cement, such as rapid hardening cement, white cement and sulfate resisting cement, are made by using additives or by variations in the manufacturing process. Cement mixed with water and sand forms cement plaster. Cement mixed with water, lime and sand forms mortar.
Concrete is manufactured by mixing water, cement and aggregates into a smooth composition that is cast and allowed to harden into silicate hydrates. Aggregates or fillers are any appropriate particulate matter, typically sand, gravel or crushed stone, or soil. The construction industry has taken considerable strides forward over the last two or three decades with regard to improving compressive strength of cement products, by adding materials called pozzolans that are capable of setting and hardening under water. The most commonly used pozzolans in the industry today are by-products of other industries, such as coal fly-ash, blast furnace slag, rice hull ash, silica fume, or metakaolin. Other suitable pozzolanic materials include gypsum, gypsum fines, portland cement, cement kiln dust, lime dust, stone dust, and plaster of Paris. Another approach is adding additives as plasticizers and superplasticizers.
Cement manufacture requires enormous heat and consumes a great deal of energy. The process of manufacturing cement also generates large quantities of CO2 that pollutes the earth's atmosphere. The burning of fossil fuels to heat the kiln to make cement causes greenhouse gases that are harmful to the environment and releases particulates into the air that makes breathing difficult. For every ton of cement produced, roughly ½ a ton of CO2 (greenhouse gas) is released by the burning fuel, and an additional ½ ton is released in the chemical reaction that changes raw material to clinker, making the production of cement responsible for more than 8% of carbon dioxide emissions globally. Thus, cement manufacture is expensive not just to the consumer, but to the atmosphere as well. There is increased pressure for cement producers to comply with legislation regarding emissions.
Due to economic and environmental concerns, different methods of making cement products are being considered. One method to achieve the goal of reducing carbon dioxide emissions and greenhouse gases is to formulate cements using a lower portion of calcinated material, thereby reducing carbon dioxide emissions per unit of product. As cement and gypsum are expensive, there is a need to reduce costs by using less cement and/or gypsum for the same requirements, i.e., without compromising on the strength of the material and the pressure loads it can withstand. Thus, there is a need for methods and compositions that increase the compressive strength of cement and the flexural strength of gypsum products so that less cement or gypsum is needed for the same requirements, reducing cement production and the concomitant release of CO2 into the atmosphere. As cement manufacture is energy intensive, using less cement would also have the beneficial effect of saving energy and reducing pollution.
Accordingly, a need exists for improved cement and gypsum products that have increased compressive strength and/or flexural strength yet include a lower percentage of cement and/or gypsum than standard cement or gypsum products, which is economical, durable, suitable for all types of applications, and benefits the environment.
Additionally, a need exists for improved cement and gypsum products that permit use of less expensive aggregates to reduce the cost of the cement product.